It is important in distinguishing nephropathies and uropathies to analyze the particles appearing in urine such as erythrocytes, leukocytes, epithelial cells, urinary casts, and bacteria. For example, erythrocytes are important in determining the presence or absence of bleeding in a path from the glomerulus of a kidney to the urethra. Also, increase in the number of leukocytes suggests inflammations or infections. In addition, by examining the morphology of erythrocytes or urinary casts, the derivation site thereof can be inferred.
Conventionally, as a technique for analyzing particles appearing in urine, a method has been used in which a stained urine specimen is mounted on a slide glass or a calculation board for observation with a microscope and the number of particles within the field of view are counted for each type of the particles. However, such a technique is a manual method, and imposes a burden on a person that uses the method. Moreover, variation tends to occur in the result of counting depending on the degree of the skill that the person who uses the method has.
In recent years, a technique has been developed in which the particles contained in urine are automatically classified and counted with the use of the flow cytometry method. With this method, a sample liquid prepared by performing fluorescence staining on a urine specimen is made to flow through a flow cell, and a laser beam is radiated into the flow cell. Then, the intensities of the forward scattered light and the fluorescence emitted from a particle in the sample liquid irradiated with the laser beam are measured. The intensity of the forward scattered light reflects the size of the particle. The larger the particle is, the larger the intensity of the forward scattered light will be. On the other hand, the intensity of the fluorescence reflects the degree of fluorescence staining of the particle. The intensities of the forward scattered light and the fluorescence differ depending on the kind of the particles. Therefore, by making analyses while combining such optical information, the kind of the particles can be determined, and the number of the particles can be counted. Such a technique is disclosed, for example, in the specification of U.S. Pat. No. 5,325,169.
However, by the method of the above-described U.S. Pat. No. 5,325,169, with a urine sample containing yeast-like fungi which are comparatively large bacteria, the intensities of the forward scattered light and the fluorescence detected from those particles will be of the same degree as those detected from erythrocytes, thereby sometimes making it difficult to distinguish the yeast-like fungi from the erythrocytes.
To such a problem, there is for example a method in which a result of measuring a sample liquid, which is prepared by adding a cell membrane damaging agent for hemolyzing the erythrocytes to a specimen containing erythrocytes and yeast-like fungi, with a flow cytometer, and a result of measuring a sample liquid prepared without adding the cell membrane damaging agent with a flow cytometer are obtained and compared so as to distinguish the erythrocytes from the yeast-like fungi and to count the number of the erythrocytes. Such a technique is disclosed, for example, in Japanese Patent Application Laid-Open (JP-A) Patent Publication No. H09-329596.
However, by the method disclosed in Japanese Patent Application Laid-Open (JP-A) Patent Publication No. H09-329596, a sample with hemolyzed erythrocytes and a sample without hemolyzing the erythrocytes are respectively measured, thereby increasing the amount of the specimen and the reagents needed for the measurement, and also increasing the time needed for the measurement.